1. Field of the Invention
This invention relates to novel crystalline chromosilicates and to their use. More particularly, this invention relates to novel chromosilicate crystalline molecular sieve materials having catalytic properties and to various hydrocarbon conversion processes using such crystalline chromosilicates. The field of art can, in part, be found in U.S. Patent Class 423-326, 252-458 and 260-668.
2. Description of the Prior Art
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic capabilities for many hydrocarbon processes. Certain zeolitic materials are ordered porous crystalline aluminosilicates having a definite structure with large and small cavities interconnected by channels. The cavities and channels throughout the crystalline material are generally uniform in size, allowing certain hydrocarbons to be selectively adsorbed giving one of the practical utilities to these materials. Consequently, these materials in many instances have come to be classified in the art as molecular sieves and are utilized, in addition to the adsorptive selective processes, for certain catalytic properties. The catalytic properties of these materials are also affected in some instances by the size of the molecules which are allowed selectively to penetrate the crystal structure presumably to be contacted with active catalytic sites within the ordered structure of these materials.
Generally the term "molecular sieve" includes a wide variety of positive ion containing crystalline materials of both natural and synthetic varieties. They are generally characterized as crystalline aluminosilicates, although other crystalline materials are included in the broad definition. The crystalline aluminosilicates are made up of networks of tetrahedra of SiO.sub.4 and AlO.sub.4 moieties in which the silicon and aluminum atoms are cross-linked by the sharing of oxygen atoms. The electrovalence of the aluminum atom is balanced by the use of a positive ion, for example, alkali metals or alkaline earth metals.
Prior art developments have resulted in the formation of many synthetic crystalline materials. Crystalline aluminosilicates are the most prevalent and, as described in the patent literature and in the published journals, are designated by letters or other convenient symbols. Exemplary of these materials are Zeolite A (U.S. Pat. No. 2,882,243), Zeolite X (U.S. Pat. No. 2,882,244), Zeolite Y (U.S. Pat. No. 3,130,007), Zeolite ZSM-5 (U.S. Pat. No. 3,702,886), Zeolite ZSM-11 (U.S. Pat. No. 3,709,979), Zeolite ZSM-12 (U.S. Pat. No. 3,832,449), and others.
Especially relevant art is the above U.S. Pat. No. 3,702,886, claiming the crystalline aluminosilicate Zeolite ZSM-5 and the method for making the same. This patent is limited to the production of a zeolite wherein aluminum or gallium oxides are present in the crystalline structure along with silicon or germanium oxides. A specific ratio of the latter to the former are reacted to produce a class of zeolites designated ZSM-5 all limited to crystalline alumino- or gallo-silicates or germanates and having a specified X-ray diffraction pattern. The above ZSM-11 and ZSM-12 patents are similarly limited to crystalline alumino- or gallo-silicates or germanates also having specified X-ray diffraction patterns.
Manufacture of the ZSM materials utilizes a mixed base system in which materials such as sodium aluminate and a silica-containing material are mixed together with sodium hydroxide and an organic base, such as tetrapropylammonium hydroxide and tetrapropylammonium bromide, under specified reaction conditions to form the crystalline aluminosilicate material having a specific X-ray diffraction pattern.
Other relevant art includes U.S. Pat. Nos. 3,329,480 and 3,329,481, which relate to "zircono-silicates" and "titano-silicates" respectively.
The present invention, however, relates to a novel family of stable synthetic crystalline materials characterized as chromosilicates identified as AMS-1Cr and having a specified X-ray diffraction pattern. The claimed AMS-1Cr crystalline chromosilicates are formed by reacting a chromium salt and a silicon-containing material in a basic medium. The product formed contains very little aluminum atoms in its crystalline network.